Lec44 Cestodes and trematodes Flashcards
What are the two different types of platyhelminthes?
cestodes = taenia [flatworms] trematodes = schistosomes [flukes]
What are characteristics of cestodes?
- flat, ribbonlike worms
- can be many meters in length
- each segments has set of male and female organs = independent reproductive units
What is the scolex of a cestodes?
- head of worm, has crown of hoooklets [rostellum] and attaching suckers
What are proglottids of cestodes?
a proglottid = a segment of cestode
How do cestodes grow?
- grow from scolex in neck region by strobilization
= process of formation of new proglottids which displaces previous ones toward period end –> immature are toward front, mature toward back - farthest back ones become gravid = have uterus filled with eggs
- gravid proglottids detach from worm —> exit host in feces or by spontaneous migration
What is lifecycle of cestodes?
- eggs or gravid prglottids in feces and passed in environment
- cattle and pigs infected by ingesting contaminated vegetation
- oncospheres hatch, penetrate intsetine wall and circulate to muscle
- oncospheres develop into cysticerci in muscle
- humans infected by ingesting raw/undercooked meat
- scolex attaches to intestine
- adults in small intestine
and repeat
What is name of fish tapeworm?
diphyllobothrium latum
How do you treat flatworms?
generally single dose of praziquantel
What are clinical signs of diphyllobothrium latum?
- get it from eating fish
- rare cause of macrocytic anemia from B12 deficiency
What are characteristics of T. saginata?
- beef tapeworm
- no hooks in scolex [head]
- uterine branches are greater in number in the proglottid
What are characteristics of T. solium?
- pork tapeworm
- scolex with hooklets
- uterine branches fewer in number in the proglottid
What is geo distribution of taenia solium?
- worldwide distribution
- most common in countries with poverty, poor sanitation, close contact with pigs
What kind of tapeworm would you get from eating pork?
taenia solium
What is number one cause of adult-onset seizures in developing world?
parasitic infection
What is neurocysticercosis? cause? signs?
- due to ingestion food/water contaiminated by feces of person infected by pork tapeworm [taenia solium]
- onchospheres hatch and disseminate to larval stage in brain/skeletal muscle/subcutaneous tissue
- see adult onset seizures, lucencies in brain
What are possible complication of taenia solium?
- neurocysticercosis [seizures]
- acute blindness
What is treatment for neurocysticercosis?
- surgery when ventricles involved
- for 5-100 lesions –> give albendazole + steroids
What are the two benzimidazoles?
- albendazole
- mebednazole
What is advantage of benzimidazoles over praziquantel?
- lower cost
- improved penetration in subarachnoid space
- increased drug levels when given with corticosteroids
What is mech of action of benzimadzoles?
- inhibit assemby microtubules and inhibit uptake of glucose by helminths
- parasite immobilization and death
- larvacidal
What is mech of action of praziquantel?
- damages worm integument [coating]
- allows for influx of Ca ions
What are most flat worms and flukes treated with?
praziquantel
What do benzimidazoles treat?
- round worms
- larval forms of flat worms
What causes a hydatid cyst?
- ingestion of feces contaiminated with eggs of dog tapeworm [echinococcus granulosus]
What is pathogenesis of hydatid cyst?
- dog tapeworm larvae hatch, penetrate small intestine, migrate via bloodstream to live, lung, brain
What are signs of hydatid cyst?
- water lilly sign on xray
- salty taste in mouth when couping
What is normal life cycle of dog tapeworm? with human?
- adult in small intestine of dog
- eggs in feces can be consumed by sheep
- oncosphere hatches, penetrates intestinal wall, hydatid cyst,
- have dissemination of larval form –> dog can consume some of sheep
humans take place of sheep when ingest some of eggs by accident
How do you get adult pork tapeworm infection? larval?
adult from eating pork
larval from feces
What are complications of hydatid cyst?
- cyst expansion can rupture into biliary tree
- erode through diaphragm to pleural cavity
- rupture to peritoneum
- cause anaphylaxis due to release pathogen antigens
What is vomica?
- salty taste after rupture of hydatid cyst leads to metastatic spread of daughter cysts
What is treatment for echinococcus granlusosus infection?
in liver –> PAIR procedure [percutaenous, aspiration, installation, re-aspiration
in lung –> surgical excision first choice, albendazole second choice
What is PAIR proceudre?
go through skin to cyst
aspirate out some of fluid
then reinstill hypertonic saline/alcohol that will kill off whatevers left in the cyst
then re-aspirate to get rid of rest of cyst material
What animals does E. granulosus infect?
sheep and dogs = sheepherders disease
What are characteristics of trematodes?
- similar to flatworms but usually nonsegmented
- share common part of lifecycle that must pass through a snail
- most hermaphrodotic
- eggs include lid-like structure [operculum]
What are two different disease manifestations of T. solium? source?
from eating undercooked pork –> tapeworm in instestine: weight loss, loss of nutrients
from food contaminated by feces of an infected human –> eggs: neuro disease
What is exception to the rule that trematodes contain both male and female reproductive organs [are hermaphroditic]?
schistosomes
What is geo distribution of s. mansoni?
- through tropics, most prevalent Africa and Brazil
What are the two liver/intestinal flukes?
- s. mansoni
- s. japonicum
What is the name of the bladder fluke?
- s. haematobium
What are characteristics of schistomiasis? how long do parasites live? cause of pathology?
- 200 million infected
- parasites long lived
- pathology due to egg-induced granuloma formation in affected organs
What are clinical sigsn of schistomiasis?
- depends on species
- splenomegaly, hepatomegaly, portal HT
- hematuria, bladder cancer
- CNS involvement
- cercarial dermatitis
Where is S. haematobium? source of infection?
- throughout Africa
- infection via freshwater in south/subsaharan africa, nile river valley
Where is S. japonicum?
- in indonesia, parts of china and SE Asia
Where is S. mekongi?
- in cambodia and laos
Where is S. intercalatum?
central and west africa
What is life cycle of schistomiasis?
- eggs in water –> hatch releasing miracidia
- piracidia penetrate snail tissue –> have sporocysts in snails –> ercariae released by snail into water and free swim
- ercariae penetrate human skin –> enter circulation –> migrate to portal blood in liver and mature –> migrate to rectum and lay eggs that circulate to liver and shed in stools or urine
What is immune reaction to schistosoma eggs? What is problem with this
intenseTH2 rxn = get scarring of bladder or liver [wherever eggs are shed]
How do schistosoma evade immune response?
- incorporate host proteins into tegument
- suppress CD4 T cell activation by impairing APC-T cell interaction
What is relationship CD4 and schistosoma development?
- CD4 T cells promote parasite development and egg production
What is effect of S. mansoni and HIV co-infection?
- reduced fecal egg excretion correlating with lower CD4
What are clinical symptoms common to all schistosomas?
- anemia and malnutrition
- cough, fever, fatigue
- rarely –> CNS manifestations from embolization of eggs
What are signs of schistosoma intestinal disease?
- ab pain, diarrhea, hepatosplenomegaly [due to scarring], portal hypertension, pulm HT
What are signs of urogenital intestinal disease?
- hematuria, lesions of cervix/vagina, pain during intercourse, pathology of seminal vesicles, infertility, bladder fibrosis
What is swimmers itch [cercarial dermatitis]?
due to exposure of our skin to cercaria of avian schistosomes in freshwater fish/stream
just get itchiness, no penetration
How do schistosomes travel once inside human?
- via mesenteric venules
What are signs of schistoma mansoni?
- commonly in liver = pipestem fibrosis
- eggs can also migrate to lungs or spinal cord
- under microscope see granuloms
What are signs of schitosoma hematobium?
- mature in GU venous plexuses instead of portal circulation
- present as asymptomatic hematuria
- later disease from bladder wall scarring –> obstructive uropathy
- terminal spine on egg
Which schistosome eggs have lateral vs terminal spine?
- S. mansoni = lateral spine
- S. hematobium = terminal spine
How do you treat schistosomiasis?
praziquantel
What is opistorchis [clonorchis] sinensis? What do you get it from?
- chinese liver fluke
- associated with eating raw fresh water fish esp East Asia
What is pathogenesis of opistorchis sinensis infection?
- goes to bile ducts after penetrating intestinal wall
- causes chronic inflammation –> increased risk cholangiocarcinoma [bile duct cancer]
What are characteristics of fasciola hepatica?
- require snail as intermediate
How do you get fasciola hepatica?
- human infected when eat raw watercress
What is the one trematode you don’t treat with praziquantel?
fasciola hepatica
What is pathogenesis of fasciola hepatica?
- eggs leave human feces and infect water
- cercariae leave snail and attach aquatic vegetation
- larvae penetrate intestinal wall to enter liver parenchyma and eventually bile ducts
How do you treat fasciola hepatica?
- triclabendazole
What are the 3 liver flukes of note?
- F. hepatica
- F. buski
- O. sinensis
What is paragonimus westermani? how is it acquired?
- lung fluke
- acquired by eating raw infected shellfish in east asia
What is pathogenesis/signs of lung fluke infection?
- cycstic cavities in lungs mimic tuberculosis
- eosinophilia
- migrating larval worms can invade spinal cord/brain
What is lifecycle of paragonimus?
- ingest by humans –> intestine –> penetrates diaphragm –> adult lives in cystic cavities in lungs –> produce eggs that are released in feces and sputum
- -> embryonated egg in water penetrate snail –> go to crustaceans –> ingested by hyman
